AC Milan were held to a 0-0 home draw by Bologna, leaving them one point clear at the top of Serie A.
Wins by defending champions Inter Milan and second-placed Napoli at the weekend put pressure on Milan to respond.
But the hosts struggled, with French forward Olivier Giroud's header, well saved by Lukasz Skorupski, their best first-half effort.
Zlatan Ibrahimovic came off the bench after the break, but Bologna withstood late pressure to seal a point.
Bologna, in 12th place, were without coach Sinisa Mihajlovic on the touchline as he undergoes hospital treatment for leukaemia.
Milan have seven games left as they pursue their first Scudetto since 2011.
